RE: Rest for helical fletching????
ArthurP is correct.
As for the rest.If you are going to use full helical why not use a drop-away rest?
I was skeptical of the dropaways till I tried one,now I don't know if I'll ever go back to a conventional rest.
Check them out they may be the answer,Trophy Taker,MZE,ARC system, or convert a GK rest they work fantastic.